The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention relates to encapsulated toner compositions comprised of a core containing a binder resin, and colorants, including pigments, dyes, or mixtures thereof, and a polymeric shell thereover preferably prepared by interfacial polymerization. The polymeric shell contains a soft, flexible component such as a polyether moiety primarily for the purpose of improving the packing of the shell materials. Proper packing of the shell components permits, for example, a high density shell structure, and lowers, suppresses, or in some instance may eliminate the shell's permeability especially to the core binders. A high degree of shell permeability is primarily responsible for the leaching or bleeding of core binder from the toner, causing the problems of toner agglomeration or blocking, and image ghosting in imaging and printing processes, which problems are avoided or minimized with the toners of the present invention. A specific embodiment of the present invention relates to encapsulated toner compositions comprised of a core of binder resin and colorants, which core is encapsulated by a polymeric shell such as a polyurea, polyamide or polyester having incorporated within its structure a soft polyether or other similar component whereby there are enabled toners with the advantages illustrated herein including the absence or minimization of toner agglomeration, and the absence or minimization of image ghosting. Another specific embodiment of the present invention relates to an encapsulated pressure fixable toner composition wherein the shell is comprised of the reaction product of a polyisocyanate or polyisocyanates selected, for example, from the group consisting of benzene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, polymethylene diisocyanate, other aromatic polyisocyanates, aliphatic isocyanates, and a diamine, or polyamines as illustrated in more detail hereinafter; and which shell further contains preferably in its structure a component, preferably a polyether or other soft structural moiety to, for example, prevent or minimize leaching or loss of the core components especially the core binder. In another embodiment of the present invention, the toner compositions obtained preferably include thereon an electroconductive material thereby enabling compositions with a controlled and stable volume resistivity such as, for example, from about 1.times.10.sup.3 to about 1.times.10.sup.8 ohm-cm, and preferably from about 5.times.10.sup.4 and 5.times.10.sup.7 ohm-cm, which toners are particularly useful for inductive development processes.
Examples of advantages associated with the toner compositions of the present invention are as indicated herein, and include the elimination and/or the minimization of image ghosting, excellent fixing characteristics, acceptable surface release properties, in some instances enabling their selection, for example, in imaging systems wherein a release fluid such as a silicone oil is avoided, substantially no toner agglomeration, acceptable powder flow characteristics, and minimal or no leaching of the core components. Also, the toners of the present invention possess the advantages of the ability to provide a substantially higher image fix to plain paper in some instances; a shell with substantially improved mechanical properties; and moreover, the shell monomers selected possess in many instances low vapor pressures, thus reducing environment hazards, which is not the situation with some of the prior art toner shells. Further, with the toner compositions of the present invention, the shell does not rupture prematurely causing the core component comprised, for example, of a polymer and magnetite, or other pigment to become exposed, which upon contact with other toner particles or toner development subsystem component surfaces and the like forms undesirable agglomerates. The excellent surface release properties possessed by the toners of the present invention provide for a complete or substantially complete transfer of toned images to a paper substrate during the development process, thus rendering this process very efficient. Furthermore, the toner compositions of the present invention can be obtained in high reaction yields in several embodiments thereof, and simple washing procedure to remove the coarse and fine particles can be selected to lower the manufacturing cost thereof. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. Preferably the toner compositions of the present invention are selected for pressure fixing processes for ionographic printing wherein dielectric receivers, such as silicon carbide, are utilized, reference U.S. Pat. No. 4,885,220 entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference. Specifically, the toner compositions of the present invention can be selected for image development in commercial Delphax printers such as the Delphax S9000, S6000, S4500, S3000, and Xerox Corporation printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized, that is fixing of the developed image is accomplished by simultaneously transferring and fixing the developed images to a paper substrate with pressure. Another application of the toner compositions of the present invention is for two component development systems wherein, for example, the image toning and transfer are accomplished electrostatically, and the fixing of the transferred image is achieved by application of pressure, with or without the assistance of thermal energy.
The toner compositions of the present invention can, in one specific embodiment, be prepared by interfacial polymerization involving microcapsule shell-forming polycondensation, followed by an in situ core binder-forming free-radical polymerization of a core monomer or monomers in the presence of a free-radical initiator and suitable colorants. Thus, in one embodiment the present invention is directed to a process for a simple and economical preparation of pressure fixable encapsulated toner compositions by interfacial/free-radical polymerization methods wherein there are selected core monomers, pigments, and shell monomers, with at least one of the shell monomers containing a polyether segment therein, and a free radical initiator. Other process embodiments of the present invention relate to, for example, interfacial/free-radical polymerization methods for obtaining encapsulated colored toner compositions. Further, in another process aspect of the present invention the encapsulated toners can be prepared in the absence of solvents thus eliminating explosion hazards associated therewith; and furthermore, these processes do not require expensive and hazardous solvent separation and recovery steps. Moreover, with the process of the present invention there are obtained improved yields of toner products since, for example, the extraneous solvent component can be replaced by liquid core monomer(s). The toners prepared in accordance with the process of the present invention are useful for permitting the development of images in reprographic imaging systems, inclusive of electrostatographic and ionographic imaging processes wherein pressure fixing is selected, and for other imaging and printing processes.
The toner compositions of the present invention contain unique shell materials that permit the containment or substantial retention of the core components, thus eliminating or substantially suppressing core binder diffusion and leaching. As a consequence, the problems of toner agglomeration and image ghosting are completely or substantially eliminated. Furthermore, the toner compositions of the present invention dramatically improve the efficiency of the image transfer process to substrates such as paper in many embodiments. Also, with the toner compositions of the present invention, particularly with respect to their selection for single component inductive development processes, the toner particles contain on their surfaces a uniform and substantially permanently attached electroconductive material thereby imparting certain stable electroconductive characteristics to the particles inclusive of situations wherein these particles are subjected to vigorous agitation. With many of the prior art toners, the surface conductivity properties of the toner particles may be unstable when subjected to agitation, especially for example, when electroconductive dry surface additives such as carbon black are selected. Further, with the aforementioned prior art toner compositions there are usually obtained images of low quality with substantial background deposits, particularly after a number of imaging cycles, especially subsequent to vigorous mechanical agitation which results in toner electroconductivity instability since the additives such as carbon black are not permanently retained on the surface of the toner. Additionally, several of the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions are obtained by processes which utilize organic solvents. The utilization of organic solvents renders the preparative process costly and potentially hazardous since most organic solvents are flammable and explosion-prone, and such processes also require expensive solvent separation and recovery steps. Moreover, the inclusion of solvents also decreases the toner throughput yield per unit volume of reactor size. Furthermore, with many of the prior art processes toners of narrow size dispersity cannot be easily achieved as contrasted with the process of the present invention where narrow particle size distributions are generally obtained. In addition, many prior art processes provide deleterious effects on toner particle morphology and bulk density as a result of the removal of solvent and the subsequent collapse or shrinkage of toner particles during the toner work-up and isolation processes resulting in a toner of very low bulk density. These disadvantages are substantially eliminated with the toners and processes of the present invention. More specifically, thus with the encapsulated toners of the present invention control of the toner physical properties of both the core and shell materials can be achieved. Specifically, with the encapsulated toners of the present invention undesirable leaching or loss of core components is avoided or minimized, and image ghosting is eliminated in many instances primarily in view of the presence of polyether functions in the shell material and the low permeability characteristics of the shell structure. Image ghosting is an undesirable phenomenon commonly encountered in ionographic printing when undesirable toner compositions are utilized. It refers to the repetitious printing of unwarranted images, and arises primarily from the contamination of the dielectric receiver by the unremovable toner materials. This problem can sometimes be partially eliminated by use of suitable surface release agents which aids in the removal of residual toner materials after image transfer. The toner compositions of the present invention eliminate or substantially eliminate the image ghosting problem by providing a microcapsule shell which effectively contains the core binder, inhibiting its leaching, and prevents it from coming into contact with the dielectric receiver during the image transfix process. In addition, the polyether component of the shell materials of the present invention also provides excellent surface release properties, thus enabling efficient removal of residual toner materials from the dielectric receiver surface. Furthermore, the excellent surface release properties afforded by the polyether-incorporated shell also dramatically enhances the image transfer efficiency of the transfix development processes.
Encapsulated cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since the toner compositions selected can be fixed without application of heat. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fixed under high pressure, which has a tendency to severely affect the fixing characteristics of the toner selected. This can result in images of low resolution or no images whatsoever. High pressure fixing also can result in unacceptable paper calendering. Also, with some of the prior art cold pressure toner compositions substantial image smearing can result from the high pressures used. Many of the prior art cold pressure fixable toner compositins, particularly those prepared by conventional melt blending processes, do not usually provide high image fix levels. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions when fixed under high pressure provide, in some instances, images which are of high gloss and of low crease and rub resistance.
There were reported in a patentability search the following prior art, all U.S. Pat. Nos.: 3,967,962 which discloses a toner composition comprising a finely divided mixture comprising a colorant material and a polymeric material which is a block or graft copolymer, including apparently copolymers of polyurethane and a polyether (column 6), reference for example the Abstract of the Disclosure, and also note the disclosure in columns 2 and 3, 6 and 7, particularly lines 13 and 35; however, it does not appear that encapsulated toners are disclosed in this patent; U.S. Pat. No. 4,565,764 which discloses a microcapsule toner with a colored core material coated successively with a first resin wall and a second resin wall, reference for example the Abstract of the Disclosure and also note columns 2 to 7, and particularly column 7, beginning at line 31, wherein the first wall may comprise polyvinyl alcohol resins known in the art including polyurethanes, polyureas, and the like; U.S. Pat. No. 4,626,490 contains a similar teaching as the '764 patent and more specifically discloses an encapsulated toner comprising a binder of a mixture of a long chain organic compound and an ester of a higher alcohol and a higher carboxylic acid encapsulated within a thin shell, reference the Abstract of the Disclosure, for example, and note specifically examples of shell materials in column 8 , beginning at line 64, and continuing on to column 9, line 17, which shells can be comprised, for example, of polyurethanes, polyurea, epoxy resin, polyether resins such as polyphenylene oxide or thioether resin, or mixtures thereof; and U.S. patents of background interest include U.S. Pat. Nos. 4,442,194; 4,465,755; 4,520,091; 4,590,142; 4,610,945; 4,642,281; 4,740,443 and 4,803,144.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169, the disclosure of which is totally incorporated herein by reference, microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure repturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions usually containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Interfacial polymerization processes are described in British Patent Publication 1,371,179, the disclosure of which is totally incorporated herein by reference, which publication illustrates a method of microencapsulation based on in situ interfacial condensation polymerization. More specifically, this publication discloses a process which permits the encapsulation of organic pesticides by the hydrolysis of polymethylene polyphenylisocyanate, or toluene diisocyanate monomers. Also, the shell-forming reaction disclosed in the aforementioned publication is initiated by heating the mixture to an elevated temperature at which point the isocyanate monomers are hydrolyzed at the interface to form amines, which then react with unhydrolyzed isocyanate monomers to enable the formation of a polyurea microcapsule wall. Moreover, there is disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, interfacial polymerization processes for pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctadecylvinylether-co-maleic anhydride as a soft component.
Furthermore, other prior art, primarily of background interest, includes U.S. Pat. Nos. 4,254,201; 4,465,755 and Japanese Patent Publication 58-100857. The Japanese publication discloses a capsule toner with high mechanical strength, which is comprised of a core material including a display recording material, a binder, and an outer shell, which outer shell is preferably comprised of a polyurea resin. In the '201 patent there are disclosed encapsulated electrostatographic toners wherein the shell material comprises at least one resin selected from polyurethane resins, a polyurea resin, or a polyamide resin. In addition, the '755 patent discloses a pressure fixable toner comprising encapsulated particles containing a curing agent, and wherein the shell is comprised of a polyurethane, a polyurea, or a polythiourethane. Moreover, in the '201 patent there are illustrated pressure sensitive adhesive toners comprised of clustered encapsulated porous particles, which toners are prepared by spray drying an aqueous dispersion of the granules containing an encapsulated material.
Also, there are illustrated in U.S. Pat. No. 4,280,833 encapsulated materials prepared by interfacial polymerization in aqueous herbicidal compositions. More specifically, as indicated in column 4, beginning at line 9, there is disclosed a process for encapsulating the water immiscible material within the shell of the polyurea, a water immiscible organic phase which consists of a water immiscible material, that is the material to be encapsulated, and polymethyl polyphenyl isocyanate is added to the aqueous phase with agitation to form a dispersion of small droplets of the water immiscible phase within the aqueous phase; and thereafter, a polyfunctional amine is added with continuous agitation to the organic aqueous dispersion, reference column 4, lines 15 to 27. Also of interest is the disclosure in column 5, line 50, wherein the amine selected can be diethylene triamine, and the core material can be any liquid, oil, meltable solid or solvent soluble material, reference column 4, line 30. A similar teaching is present in U.S. Pat. No. 4,417,916.
In U.S. Pat. No. 4,599,271, the disclosure of which is totally incorporated herein by reference, there are illustrated microcapsules obtained by mixing organic materials in water emulsions at reaction parameters that permit the emulsified organic droplets of each emulsion to collide with one another, reference the disclosure in column 4, lines 5 to 35. Examples of polymeric shells are illustrated, for example, in column 5, beginning at line 40, and include isocyanate compounds such as toluene diisocyanate, and polymethylene polyphenyl isocyanates. Further, in column 6, at line 54, it is indicated that the microcapsules disclosed are not limited to use on carbonless copying systems; rather, the film material could comprise other components including xerographic toners, see column 6, line 54.
Other prior art includes U.S. Pat. No. 4,520,091, the disclosure of which is totally incorporated herein by reference, which illustrates an encapsulated toner material wherein the shell can be formed by reacting a compound having an isocyanate with a polyamide, reference column 4, lines 30 to 61, and column 5, line 19; and U.S. Pat. No. 3,900,669 illustrating a pressure sensitive recording sheet comprising a microcapsule with polyurea walls, and wherein polymethylene polyphenyl isocyanate can be reacted with a polyamide to produce the shell, see column 4, line 34.
Liquid developer compositions are also known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments, and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as polyvinyl pyrrolidone. Additionally, there is described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1, and 2 thereof.
Illustrated in a U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676, (now abandoned) the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
There is a need for encapsulated toner compositions with many, and in some embodiments substantially, if not all, the advantages illustrated herein. More specifically, there is a need for encapsulated toners with shells that eliminate or minimize the loss of core components such as the binder resin. Also, there is a need for encapsulated toners wherein images with excellent resolution and superior fix are obtained. Moreover there is a need for encapsulated toners, including colored toners wherein image ghosting, toner offsetting, and undesirable leaching of core components and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with, in some instances, excellent surface release characteristics enabling their selection in imaging systems without silicone oils and the costly apparatus associated therewith. Furthermore, there is a need for encapsulated toners, including colored toners, which exhibit no toner agglomeration thus providing a long toner shelf life exceeding, for example, one to two years, and wherein the core is encapsulated in a shell containing a soft polyether component therein. Also, there is a need for encapsulated toners that have been surface treated with additives such as carbon blacks, graphite or the like to render them conductive to a volume resistivity level of preferably from about 1.times.10.sup.3 to 1.times.10.sup.8 ohm-cm, and to enable their use in single component inductive development systems. Further, there is a need for encapsulated toners wherein surface additives such as metal salts or metal salts of fatty acids and the like are utilized to primarily assist in toner surface release properties. There is also a need for processes for the preparation of encapsulated toners with the advantages described hereinbefore. Specifically, there is a need for interfacial polymerization processes for black and colored encapsulated toner compositions, wherein the core contains a colorant or colorants, and a core binder derived from in situ free-radical polymerization of an addition-type monomer or monomers, which core is encapsulated in a microcapsule shell containing a polyether component. Furthermore, there is a need for toners and improved processes thereof that will enable the preparation of pressure fixable encapsulated toner compositions whose properties such as shell strength, core binder molecular weight and the nature of core binder crosslinking can be desirably controlled. Moreover, there is a need for enhanced flexibility in the design and selection of materials for the toner shell and core, and the control of the toner physical properties, such as bulk density, particle size, and size dispersity.